The subject matter disclosed herein relates to a system and method of visual verification, and in particular to a system and method of a visual verification of an accuracy of a light projection.
Light projection devices (often referred to as “laser projection devices”) are used in a variety of applications to project images onto objects. In some applications, an illuminated three-dimensional (3D) pattern, also referred to as a “template,” are projected onto an object. The template may be formed, for example, by projecting a rapidly moving, vector-scan, light beam onto the object. In some systems, the projected light beam is a laser beam. The light beam strikes the surface of the object following a predetermined trajectory in a repetitive manner. When moved at a sufficiently high beam speed and refresh rate, the trace of the projected beam on the object appears to the human eye as a continuous glowing line. The projected pattern of light appears as the glowing template that can be used to assist in the positioning of parts, components and work pieces. In some cases, the projected template is based partly on computer aided design (CAD) data of the object.
It should be appreciated that light projection devices may have a number of calibration parameters (also referred to as compensation parameters) that may change over time. Therefore, it is desirable for the operator to have a means for verifying the accuracy of the light projection. One method of accuracy verification uses an artifact (or reference artifact) such as the artifact 10 shown in FIG. 1A. The artifact 10 is a made of a rigid and stable material of known shape and size. The artifact 10 usually has a relatively low coefficient of thermal expansion (CTE), such as aluminum or steel. A plurality of reflective markers 12 are mounted on the artifact 10. In addition, one or more geometric elements 13 are inscribed into the artifact or applied to the artifact. For example, the inscribed geometric elements 13 may include squares 14, circles 16, and diamonds 18. The inscribed geometric elements may be measured with an articulated arm coordinate measurement machine (AACMM) that includes a tactile probe having a fine probe tip. The positions of the reflective markers 12 may likewise be measured with the AACMM, possibly in combination with an additional measuring system such as a photogrammetry system or a laser tracker. The result of these measurements is to obtain 3D coordinates of the inscribed pattern 11 relative to the reflective markers 12. It should be appreciated that artifacts are relatively costly and time consuming to produce.
To verify proper operation of the light projection device, the light projection device emits light onto the artifact 10. Light reflected from the reflective markers 12 is detected by the light projection device. The light projection device further determines the angular position of each of the reflective markers 12 and, from these angular positions, determines the pose of the reference artifact 10 relative to the light projection device. The determined pose is used to determine the position of the inscribed pattern 13 relative to the light projection device. The projector then attempts to project the glowing template onto the inscribed pattern 13 (also referred to as the one or more inscribed elements 13). An operator inspects the glowing template in relation to the inscribed pattern 13 to determine whether the light projection device lies within limits of the inscribed pattern 13, thereby verifying that the light projector is performing according to its specification. For example, the light projection device may project the glowing template onto the inscribed pattern 11 that includes the geometric shapes 14, 16, 18. When the projected light template does not lie directly on the inscribed pattern 13, the operator may take additional steps to have the light projection device serviced or calibrated.
In many cases, users would prefer to perform calibration of reference artifacts on site rather than returning the artifacts back to a manufacturer's calibration laboratory. In other cases, users would prefer larger artifacts than are commercially available from a manufacturer. In still other cases, users would prefer a more flexible way of creating reference artifacts.
Accordingly, while existing systems and methods of verifying the accuracy of a light projection device are suitable for their intended purposes, the need for improvement remains, particularly in providing a system and method of verifying the accuracy of a light projection, such as for creating artifacts in a flexible manner or obtaining artifacts that are larger than are available commercially. The need also remains for obtaining calibration of artifacts in a cost-effective manner.